2017 ASHS Annual Conference

The International Sweet Corn Development Association (ISCDA) formed a committee in the late 1980’s to address stand establishment problems in the new “supersweet” hybrids that were becoming popular at the time. These hybrids incorporate the mutant endosperm gene, shrunken-2 (sh2), which interferes with starch synthesis so that sugars accumulate in the kernel. Supersweets are attractive to sweet corn producers, shippers, processors, and consumers because they retain sweetness long after harvest. Unfortunately, they germinate poorly and have low vigor and reduced stands when compared with standard sugary (su) hybrids. Their seed is inherently weak because of low starch reserves and they have a fragile pericarp that makes them prone to fungal pathogen invasion. Some of these problems are reduced by planting in favorable environments and using seed treatments. The ISCDA Seed Treatment Committee established a trial in 1989 to identify optimum seed treatment mixtures for improving stands of sh2 sweet corn across diverse planting environments. The results proved very useful, so the committee has been organizing an annual seed treatment trial that is carried out at locations across the United States for more than 20 years. It is a cooperative effort of seed treatment manufacturers, sweet corn seed companies, processors, and university-based researchers; I am the research coordinator for the committee. The trial set the standard for sweet corn seed treatment, and continues to do so as old treatments are discontinued and new active ingredients come on the market. These trials have shown that the most effective seed treatments include 1) broad-spectrum, protectant fungicides (ex. captan, fludioxonil, thiram); 2) systemic fungicides with activity against internally-borne Fusarium moniliforme, Pennicillium ultimum, and Rhizopus species as well as soilborne Rhizoctonia solani; and 3) an oomycete product that will control soil-borne Pythium ultimum, especially in cold and wet soils (ex. metalaxyl, ethaboxam). Optimum seed treatment mixtures continue to evolve as new problems or situations arise. There is new interest in seed treatments with unique modes of action to control Pythium, because metalaxyl-resistant Pythium isolates are being found in some areas where sweet corn is grown. Systemic insecticides (ex. clothianidin, imidicloprid, thiamethoxam) are being added to seed treatment mixtures in some areas due to increasing problems with soil insects like seedcorn maggots and wireworms. The need for seed treatments that can be used in organic production systems has increased with expanded organic sweet corn acreages. These newer concerns are being addressed with the latest trials.